In recent years, electronic devices such as smartphones and tablet computers have become widespread. In the electronic devices, display devices having a touch detection function have been employed.
In a display device having a touch detection function in which a capacitive system is employed, for example, drive electrodes and detection electrodes formed in a stripe fashion are provided so as to intersect each other. When a finger is in contact with the screen of the display device having a touch detection function, the capacitance (value) changes in the portion in which the drive electrode intersects the detection electrode. In a capacitive system, contact with a finger on the screen can be detected by using the change in capacitance.
With respect to display devices having a touch detection function in which a capacitive system is employed, a technology for reducing the thickness of each device and improving the image quality by using electrodes (common electrodes) for image display in the pixels arrayed in a two-dimensional manner as the above drive electrodes is suggested.
In this technology, a display period in which display operation for image display is performed and a touch detection period in which touch detection operation for touch detection is performed are alternately provided in each period (frame period) for displaying the image of a single frame. Before and after each frame period, display adjustment periods called a perpendicular back porch period and a perpendicular front porch period are provided.
When the refresh rate (frame rate) of an image (video) in the normal driving of a display device having a touch detection function is, for example, 60 Hz, the display device may be driven at low speed with, for example, a refresh rate of 30 Hz, to reduce power consumption.
In this case, each frame period is longer than that in normal driving. However, low-speed driving may be realized by, for example, extending each display adjustment period without changing the above display period or touch detection period.
Since touch detection operation is not performed in each display adjustment period, the sensitivity for touch detection (report rate) is decreased when each display adjustment period is extended.